共查询到20条相似文献,搜索用时 31 毫秒
1.
M. W. Rotach 《Boundary-Layer Meteorology》1993,65(1-2):1-28
2.
Derivation of the aerodynamic roughness parameters for a Sahelian savannah site using the eddy correlation technique 总被引:1,自引:0,他引:1
Vertical exchange of heat, moisture and momentum above the earth's surface depends strongly on the turbulence generated by surface roughness. This roughness is best specified through the roughness length and the zero plane displacement. The ratio of windspeed to friction velocity was measured at four heights using the eddy correlation technique at a fallow savannah site in the Sahel. The change in this ratio with height was used to derive the zero plane displacement and the roughness length of the surface, together with an estimate of the error in each parameter. These were estimated as 0.93 ± 0.35 m and 0.17 ± 0.01 m, respectively. The method appears to be a more robust alternative to wind profile derivation. 相似文献
3.
城市下垫面空气动力学参数的确定 总被引:10,自引:1,他引:9
分析近10年北京325m气象塔常年观测资料,研究城市化发展对城市大气边界层动力学结构和特征的影响.结果表明,空气动力学粗糙度和零平面位移总体是逐年递增的.气象塔西南方向的高层建筑群是20世纪90年代初期逐渐建成,在SW方向,空气动力学粗糙度和零平面位移在90年代增加明显,增加的幅度1997年和1999年之间较大,这一点与气象塔西南方向城市化的加快相符合.而在NE、SE和NW方向,从1987年到1994年空气动力学粗糙度和零平面位移增加明显,1994年以后变化较小. 相似文献
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冬季北京城市近地层的气象特征 总被引:14,自引:1,他引:14
运用2001年1~3月北京大气边界层和大气化学综合试验期间,中国科学院大气物理研究所铁塔上所获得的8~320 m 15层风、温度和湿度梯度资料,对冬季北京城市边界层特征进行了诊断分析.结果表明,在冬季北京城市边界层中,平均而言地表粗糙度为1.34、零平均位移约为20 m;温度基本上随高度呈线性变化;风速随高度的变化并不总遵循对数关系,尤其是在午前和夜间,风速与高度之间对数关系的不显著率可达30%~40%.不能简单套用在Monin-Obuhov相似理论中由Businger-Dve风廓线层结订正获得的近地面层动量、热量和水汽湍流输送计算公式. 相似文献
6.
利用2013年7月1日至2014年6月30日鄱阳湖东岸70 m铁塔涡动相关观测资料,应用Martano方法和TVM(Temperature Variance Method)方法分别计算了该地地表零平面位移d和粗糙度z0,通过代回Monin-Obukhov相似性理论的风廓线关系计算摩擦速度,以验证与实测摩擦速度的一致性。速度和温度标准差的归一化拟合线分别与Panosky等和Tillman给出的曲线趋势一致,表明该站观测数据总体满足近地层相似性。Martano方法计算结果随季节变化较大,春夏季的粗糙度是秋冬季的6.3倍;陆面方向零平面位移和粗糙度分别为来自湖面的2倍和10倍;Martano方法比TVM方法对季节和方向的敏感性更强。Martano方法计算得到零平面位移和粗糙度对摩擦速度造成了约9.9%的高估;而TVM方法对摩擦速度造成了约32.8%的高估;Martano方法计算的摩擦速度和观测值的一致性更好。 相似文献
7.
本文利用位于南京市郊区的南京大学仙林校区SORPES观测站多层湍流观测数据分析了湍流谱特征,以白天不稳定条件下垂直速度能谱谱峰对应的长度尺度也就是离地高度为判据,探讨了运用该方法确定复杂下垫面零平面位移的可行性。统计分析表明,该方法确定的长度尺度呈现出较为一致的概率分布形状,概率最大的长度尺度对应于离地高度,在复杂下垫面情况下这个高度就是零平面位移高度到观测高度之间的距离,将观测点的离地高度减去这个距离就能得到零平面位移。本文同时运用不稳定条件下垂直速度方差在近地层中的相似关系来确定零平面位移,并与谱方法得到的结果进行对比。结果表明,谱方法和方差法得到的零平面位移非常接近。 相似文献
8.
气象高塔数据资料弥足珍贵, 对其进行质量控制将为后续科学研究和业务工作的开展提供便利; 此外, 利用塔基观测资料计算空气动力学参数有助于校正模式空气动力学参数理论值。对2017-2018年深圳356 m气象梯度观测塔共13层的每10 s风速、风向、相对湿度、温度探测资料进行数据质量控制, 基于莫宁-奥布霍夫相似理论和数据质量控制后的气象梯度观测塔近地层(10 m、20 m、40 m、50 m和80 m) 1分钟平均的风温资料, 利用最小二乘法拟合迭代计算了近中性条件下深圳气象梯度观测塔下垫面空气动力学粗糙度(z0)和零平面位移(d)。结果表明:深圳气象梯度观测塔的气象探测资料数据质量很高, 连续两年平均数据缺失率为1.28%, 数据错误率为0.01%。近中性边界层条件下, 深圳气象梯度观测塔下垫面空气动力学粗糙度均值为0.35 m, 零平面位移均值为5.33 m, 结果合理可信。研究表明空气动力学参数受下垫面非均匀性、植株柔软性、气流来向、风速等的共同影响。 相似文献
9.
A method based on Giorgi (1997a, 1997b) and referred to as ‘combined approach’, which is a combination of mosaic approach and analytical-statistical-dynamical approach, is proposed. Compared with those of other approaches, the main advantage of the combined approach is that it not only can represent both interpatch and intrapatch variability, but also cost less computational time when the land surface heterogeneity is considered. Because the independent variable of probability density function (PDF) is extended to the single valued function of basic meteorological characteristic quantities, which is much more universal, the analytical expressions of the characteristic quantities, (e.g., drag coefficient, snow coverage, leaf surface aerodynamical resistance) affected by roughness length are derived, when the roughness length (and/ or the zero plane displacement) heterogeneity has been mainly taken into account with the approach. On the basis of the rule which the PDF parameters should follow, we choose a function y of the roughness length z0 as the PDF independent variable, and set different values of the two parameters width ratio αn and height ratio γ of PDF (here a linear, symmetric PDF is applied) for sensitivity experiments, from which some conclusions can be drawn, e.g., relevant characteristic terms show different sensitivities to the heterogeneous characteristic (i.e., roughness length), which suggests that we should consider the heterogeneities of the more sensitive terms in our model instead of the heterogeneities of the rest, and which also implies that when the land surface scheme is coupled into the global or regional atmospheric model, sensitivity tests against the distribution of the heterogeneous characteristic are very necessary; when the parameterαn is close to zero, little heterogeneity is represented, andαn differs with cases, which have an upper limit of about 0.6; in the reasonable range ofαn, a peak-like distribution of roughness length can be depicted by a small value ofγ, etc.. 相似文献
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Experiments were conducted in a wind-wave tank to study the long-standing discrepancy between wind stresses over a water surface determined with the profile and eddy-correlation methods. Inasmuch as the eddy-correlation method measures the turbulence flux directly, such a discrepancy is considered as an error in the way the profile data are analyzed. Uncertainties in selections of the zero reference plane for the logarithmic velocity profile and of the value for the von Karman constant are suggested to be major sources of the error. To match the results obtained with two methods, the displacement height needs to vary with wave conditions, and the value of the von Karman constant is also discussed. 相似文献
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13.
Nijs Jan Duijm 《Boundary-Layer Meteorology》1999,91(1):1-22
Some methods are evaluated and extended to estimate roughness length and zero plane displacement height for atmospheric flow over arrays of obstacles, typically buildings. It appears that the method proposed by Bottema, with an extension to account for low density obstacle arrays, performs best. Procedures are proposed to represent irregular obstacle arrangements by a representative regular array to which Bottema's method can be applied. It is shown that this can be done without loss of accuracy, in general, roughness length can be predicted within a factor of two in more than 74% of the cases (95% reliability estimate). The methods proposed by Lettau and Raupach have been included in the evaluation. Lettau's model, which only requires input on the frontal area density, predicts roughness length unbiassed for frontal area densities up to 0.3, but predictions will be within a factor of two in more than 59% of the cases only (95% reliability estimate). 相似文献
14.
Measurements Of Turbulence Transfer In The Near-Surface Layer Over The Southeastern Tibetan Plateau 总被引:5,自引:0,他引:5
Lingen Bian Zhiqiu Gao Qiangde Xu Longhua Lu Yanjie Cheng 《Boundary-Layer Meteorology》2002,102(2):281-300
Turbulent flux measurements at Qamdo site over the Tibetan Plateau during TIPEX from May 18 to June 30, 1998 are presented. Sensible heat dominated,accounting for about 66% of the available energy (the sum of net radiation and soil heat flux) prior to the monsoon(dry period), reducing to about 31%, with latent heat increased to about 56% of available energy,in the monsoon season (wet period). Surface energy budget closure on average was about 0.80 (0.85)prior to the monsoon and 0.89 (0.76) during the monsoon using eddy correlation (profile) methods. The sum of latent and sensible heat fluxes calculated from the flux-profilemethod was smaller by about 15% than that from eddy correlation. Martano's method is used toestimate the surface aerodynamic roughness length z0 and zero plane displacement d from singlelevel sonic anemometer data, giving d = 0.12 m and z0 = 0.08 m. The overall neutral dragcoefficient (CDN) and scalar coefficient (CHN) were found to be CDN = 0.0055and CHN = 0.0059 in the southeastern area of Tibet. Their variations with the mean wind speed at 10 m are discussed. 相似文献
15.
On Shear-Driven Ventilation of Snow 总被引:1,自引:1,他引:0
Andrew Clifton Costantino Manes Jean-Daniel Rüedi Michele Guala Michael Lehning 《Boundary-Layer Meteorology》2008,126(2):249-261
A series of experiments have been made in a wind tunnel to investigate the ventilation of snow by shear. We argue that the
zero-plane displacement can be used as a convenient indicator of ventilation, and that this can be obtained from measurements
of mean velocity profiles in conditions of zero pressure gradient. Measurements made over a natural snow surface show a zero-plane
displacement depth of less than 5 mm, but practical considerations preclude extensive use of snow for these measurements.
Instead, the influence of permeability is investigated using reticulated foams in place of snow. We demonstrate that the foam
and snow have similar structure and flow-relevant properties. Although the surface of the foam is flat, the roughness lengths
increase by two orders of magnitude as the permeability increases from 6 × 10−9 to 160 × 10−9 m2. The zero-plane displacement for the least permeable foams is effectively zero, but more than 15 mm for the most permeable
foams. Our data compare well to the few studies available in the literature. By analogy to conditions over snow surfaces,
we suggest that shear-driven ventilation of snow is therefore limited to the upper few millimetres of snow surfaces. 相似文献
16.
Summary In this paper the results of an urban measurement campaign are presented. The experiment took place from July 1995 to February
1996 in Basel, Switzerland. A total of more than 2000 undisturbed 30-minute runs of simultaneous measurements of the fluctuations
of the wind vector u′, v′, w′ and the sonic temperature θ
s
′ at three different heights (z=36, 50 and 76 m a.g.l.) are analysed with respect to the integral statistics and their spectral behaviour. Estimates of the
zero plane displacement height d calculated by the temperature variance method yield a value of 22 m for the two lower levels, which corresponds to 0.92 h
(the mean height of the roughness elements). At all three measurement heights the dimensionless standard deviation σ
w
/u
* is systematically smaller than the Monin-Obukhov similarity function for the inertial sublayer, however, deviations are smaller
compared to other urban turbulence studies. The σθ/θ* values follow the inertial sublayer prediction very close for the two lowest levels, while at the uppermost level significant
deviations are observed. Profiles of normalized velocity and temperature variances show a clear dependence on stability. The
profile of friction velocity u
* is similar to the profiles reported in other urban studies with a maximum around z/h=2.1. Spectral characteristics of the wind components in general show a clear dependence on stability and dimensionless measurement
height z/h with a shift of the spectral peak to lower frequencies as thermal stability changes from stable to unstable conditions and
as z/h decreases. Velocity spectra follow the −2/3 slope in the inertial subrange region and the ratios of spectral energy densities
S
w
(f)/S
u
(f) approach the value of 4/3 required for local isotropy in the inertial subrange. Velocity spectra and spectral peaks fit
best to the well established surface layer spectra from Kaimal et al. (1972) at the uppermost level at z/h=3.2.
Received September 26, 1997 Revised February 15, 1998 相似文献
17.
A significant non-alignment between the mean horizontal wind vector and the stress vector was observed for turbulence measurements
both above the water surface of a large lake, and over a land surface (soybean crop). Possible causes for this discrepancy
such as flow distortion, averaging times and the procedure used for extracting the turbulent fluctuations (low-pass filtering
and filter widths etc.), were dismissed after a detailed analysis. Minimum averaging times always less than 30 min were established
by calculating ogives, and error bounds for the turbulent stresses were derived with three different approaches, based on
integral time scales (first-crossing and lag-window estimates) and on a bootstrap technique. It was found that the mean absolute
value of the angle between the mean wind and stress vectors is highly related to atmospheric stability, with the non-alignment
increasing distinctively with increasing instability. Given a coordinate rotation that aligns the mean wind with the x direction, this behaviour can be explained by the growth of the relative error of the u–w component with instability. As a result, under more unstable conditions the u–w and the v–w components become of the same order of magnitude, and the local stress vector gives the impression of being non-aligned with
the mean wind vector. The relative error of the v–w component is large enough to make it undistinguishable from zero throughout the range of stabilities. Therefore, the standard
assumptions of Monin–Obukhov similarity theory hold: it is fair to assume that the v–w stress component is actually zero, and that the non-alignment is a purely statistical effect. An analysis of the dimensionless
budgets of the u–w and the v–w components confirms this interpretation, with both shear and buoyant production of u–w decreasing with increasing instability. In the v–w budget, shear production is zero by definition, while buoyancy displays very low-intensity fluctuations around zero. As local
free convection is approached, the turbulence becomes effectively axisymetrical, and a practical limit seems to exist beyond
which it is not possible to measure the u-w component accurately. 相似文献
18.
卫星导风的二维傅立叶相位分析技术初步研究 总被引:5,自引:1,他引:5
给出2—D傅立叶导风技术的理论推导,并运用数值模拟进行验证。介绍了示踪云的2—D频域波谱分析技术,由谐波的相位变化一次计算出波速的两个分量,期望能避免一维导风方法因一维平移假设所引起的误差。 相似文献
19.
Summary ?The paper considers a meso-scale, adiabatic, inviscid and Boussisnesq flow of a stably stratified fluid over a three-dimensional
(3-D) meso-scale orographic barrier with elliptic contour, with special reference to a part of the Western ghats mountain
along west coast of India and on the Khasi-Jayantia hill in the northeast India. The airstream characteristics are simplified
by assuming that the upstream wind velocity (U) and buoyancy frequency (N) are constant with height. Solutions for perturbation vertical velocity (w′) and streamline displacement (η′) are expressed in terms of double integrals. These integrals cannot be evaluated exactly,
hence they have been approximated by asymptotic expansion method. Side by side solutions using numerical method have also
been obtained. The results of the study indicate that the updraft regions in the asymptotic solution are crescent shaped,
symmetrical about the axis y = 0, tilting upwind and spreading laterally with height. The study also shows that in both asymptotic solution and numerical
solution w′ and η′ fall off down wind of the barrier in the central plane (y = 0), further more in the asymptotic solution w′ and η′ fall off as x
−1. The study also indicates that the discrete updraft regions obtained in the numerical solution, when joined, take a crescent
shape.
Received November 26, 2001; accepted February 27, 2002 相似文献
20.
Abstract A parameter study is presented of the linear steady response to an elevated diabatic forcing in a Boussinesq baroclinic atmosphere. The model is two‐dimensional on the vertical plane; the basic wind is perpendicular to this plane with horizontal and vertical shear. The intensity of the circulation is sensitive to the strength of the baroclinic zone only for weak static stability. A scale analysis supports this conclusion: the importance of baroclinic effects depends on the ratio of the aspect ratio of the circulation to the aspect ratio of the baroclinic basic state. Baroclinicity also leads to a tilt of the circulation due to enhanced horizontal temperature advection, and the corresponding vertical flux of horizontal momentum. The magnitude of the latter can be large when the Richardson number approaches its critical value from above, i.e. for slightly symmetrically stable basic flows; this is true even with viscosity. The resonant limit where the Richardson number approaches the critical value for symmetric instability is also examined. For non‐zero dissipation, the critical value is smaller than that of the inviscid limit. 相似文献